1. Field of the Invention
The present invention relates to head rests of vehicle seats. More particularly, the present invention relates to head rests of vehicle seats that can increase restraint performance for heads of passengers when a vehicle collision is sensed or predicted.
2. Description of the Related Art
A head rest of a vehicle seat that can increase restraint performance for a head of a passenger when a vehicle collision is sensed or predicted is already known. Such a head rest (an active head rest) is taught, for example, by Japanese Laid-Open Patent Publication Number 11-334439.
In the known head rest, a head rest main body is arranged and constructed to be tilted or inclined. When a vehicle collision (in particular, a back-side collision) is predicted or sensed by a sensor, the head rest main body is tilted, based on a signal from the sensor, so as to move toward the passenger head. As a result, the head rest main body moves closer to the passenger head so that the passenger head can be reliably supported by the head rest main body. Thus, the passenger can be prevented from suffering a whiplash injury.
Typically, the head position of the passenger sitting on the vehicle seat differs somewhat depending on the body type and the body size of the passenger. Therefore, in the known head rest, the head rest main body is not always appropriately positioned relative to the passenger head. That is, the head rest main body cannot be previously adjusted so as to be appropriately adjacent to and aligned with the passenger head. In addition, during a vehicle collision, the head rest main body is tilted over a predetermined angle range regardless of the body type and the body size of the passenger. Consequently, when a vehicle actually collides, often times, the passenger head cannot be suitably held by the tilted head rest main body. This means that the passenger cannot be sufficiently prevented from suffering a whiplash injury.